The field of art of this invention is the one encompassing processes in which hydrogen is produced in elemental form by a chemical reaction between water in any state and a metal or metallic compound. The field is further defined in that the metal or metallic compound which is consumed (i.e. oxidized) in the above reaction is regenerated by reaction with a carbonaceous reducing composition. Thus this field is distinguished from thermochemical processes and from processes in which the metal is regenerated electrolytically. The field is further defined in that the metal or metallic compound is in liquid phase in either pure or dissolved form at process conditions.
Typical prior art related to this field of invention is described in U.S. Pat. Nos. 1,050,902 and 3,821,362.
Some of the problems existing in the prior art practice of this field of invention are as follows. In one prior art process using a liquid phase metal, that metal, tin, is present strictly in pure form. The process is continuous, with the reduction and oxidation reactions occurring at physically separate regions. Care is taken that only SnO.sub.2 is removed from the oxidation region and transported to the reduction region, and that only tin is removed from the reduction region and transported back to the oxidation region. This requires either an excess of steam in the oxidation region to ensure formation of powdered SnO.sub.2, plus the difficulty of transporting a powder, or the inclusion of a molten salt or molten oxide of another metal in the process which will float on the tin and in which the SnO.sub.2 will become either dissolved or suspended. The prior art teachings of this process also require a costly external supply of heat, either electricity or a separate furnace in heat exchange relation with the reaction regions. An excessive loss of tin has also been experienced during operation. The equilibrium points of the two reactions, which determine the degree of steam conversion to hydrogen obtainable, are determined by temperature, and the temperature is constrained by other factors such as reaction rate and cost of external heating, resulting in very limited control of reaction equilibrium being possible. This is representative of deficiencies in prior art processes for production of hydrogen.